¹S. Marchi, ²B.A. Black, ³L.T. Elkins-Tanton, ¹W.F. Bottke
¹Southwest Research Institute, Boulder, CO, United States
²City College, City University of New York, New York, NY, United States
³Arizona State University, Tempe, AZ, United States

Recent revisions to our understanding of the collisional history of the Hadean and early-Archean Earth indicate that large collisions may have been an important geophysical process. In this work we show that the early bombardment flux of large impactors (>100 km) facilitated the atmospheric release of greenhouse gases (particularly CO2) from Earth’s mantle. Depending on the timescale for the drawdown of atmospheric CO2, the Earth’s surface could have been subject to prolonged clement surface conditions or multiple freeze-thaw cycles. The bombardment also delivered and redistributed to the surface large quantities of sulfur, one of the most important elements for life. The stochastic occurrence of large collisions could provide insights on why the Earth and Venus, considered Earth’s twin planet, exhibit radically different atmospheres.

Reference
Marchi S, Black BA, Elkins-Tanton LT, Bottke WF (2016) Massive impact-induced release of carbon and sulfur gases in the early Earth’s atmosphere. Earth and Planetary Science Letters 449, 96–104.
Link to Article [doi:10.1016/j.epsl.2016.05.032]
Copyright Elsevier

¹T.S. Peretyazhko, ²A. Fox, ¹B. Sutter, ³P.B. Niles, ⁴M. Adams, ³R.V. Morris, ³D.W. Ming
¹Jacobs, NASA Johnson Space Center, Houston, TX 77058
^{2/sup>Indiana University, Bloomington, IN 47406
3NASA Johnson Space Center, Houston, TX 77058
4University of Hawaii at Hilo, Hilo, HI 96720}

Akaganeite, a Cl-bearing Fe(III) (hydr)oxide, has been recently discovered in Yellowknife Bay in Gale crater on Mars by the Mars Science Laboratory (MSL) Curiosity Rover. Akaganeite was associated with sulfate and sulfide minerals at Yellowknife Bay indicating that sulfate ions could be present in solution during akaganeite formation. The mechanism and conditions of akaganeite formation in the Yellowknife Bay mudstone are unknown. We investigated formation of akaganeite through hydrolysis of ferric chloride solution in the presence of 0, 0.01, 0.05, 0.1 and 0.2 M sulfate and at initial pH of 1.5, 2 and 4 at 90 °C. Mineralogy of the precipitated Fe(III) phases was characterized by X-ray diffraction and infrared spectroscopy. The precipitates were also acid digested to determine total sulfate and chloride contents. Akaganeite and natrojarosite formed at initial solution pH of 1.5; akaganeite, goethite and natrojarosite precipitated in initial pH 2 solutions and goethite, hematite and 2-line ferrihydrite precipitated at initial solution pH of 4. Sulfate addition did not inhibit akaganeite formation. Increasing initial solution sulfate concentrations resulted in increasing sulfate to chloride ratio in the precipitated akaganeite. Infrared spectroscopy revealed akaganeite bands at ∼2 μm (H2O combination band) and at ∼2.46 μm (OH combination band). The H2O combination band position linearly correlated with total chloride content in akaganeite. Overall, laboratory studies demonstrated formation of akaganeite at initial sulfate concentration ⩽ 0.2 M (sulfate to chloride molar ratio ⩽0.3) and pH ⩽ 2, implying that those conditions might prevail (perhaps as micro-environments) during akaganeite formation in Yellowknife Bay mudstone. The occurrence of Fe(II) sulfides (pyrite and pyrrhotite) in Yellowknife Bay mudstone is a potential acidity source. Dissolution of sulfide minerals might occur under localized oxidizing water-limiting Cl-rich conditions creating favorable environments for akaganeite formation.

Reference
Peretyazhko TS, Fox A, Sutter B, Niles PB, Adams M, Morris RV, Ming DW (2016)
Synthesis of akaganeite in the presence of sulfate:Implications for akaganeite formation in Yellowknife Bay, Gale Crater, Mars. Geochmica et Cosmochmica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.06.002]
Copyright Elsevier

¹Toni Schulz, ²Ambre Luguet, ¹Wencke Wegner, ²David van Acken,^1,3Christian Koeberl
¹Department of Lithospheric Research, University Vienna, Vienna, Austria
²Steinmann Institut of Geology, Mineralogy and Palaeontology, University of Bonn, Bonn, Germany
³Natural History Museum, Vienna, Austria

The Lonar crater is a ~0.57-Myr-old impact structure located in the Deccan Traps of the Indian peninsula. It probably represents the best-preserved impact structure hosted in continental flood basalts, providing unique opportunities to study processes of impact cratering in basaltic targets. Here we present highly siderophile element (HSE) abundances and Sr-Nd and Os isotope data for target basalts and impactites (impact glasses and impact melt rocks) from the Lonar area. These tools may enable us to better constrain the interplay of a variety of impact-related processes such as mixing, volatilization, and contamination. Strontium and Nd isotopic compositions of impactites confirm and extend earlier suggestions about the incorporation of ancient basement rocks in Lonar impactites. In the Re-Os isochron plot, target basalts exhibit considerable scatter around a 65.6 Myr Re-Os reference isochron, most likely reflecting weathering and/or magma replenishment processes. Most impactites plot at distinctly lower 187Re/188Os and 187Os/188Os ratios compared to the target rocks and exhibit up to two orders of magnitude higher abundances of Ir, Os, and Ru. Moreover, the impactites show near-chondritic interelement ratios of HSE. We interpret our results in terms of an addition of up to 0.03% of a chondritc component to most impact glasses and impact melt rocks. The magnitude of the admixture is significantly lower than the earlier reported 12–20 wt% of extraterrestrial component for Lonar impact spherules, reflecting the typical difference in the distribution of projectile component between impact glass spherules and bulk impactites.

Reference
Schulz T, Luguet A, Wegner W, van Acken D, Koeberl C (2016) Target rocks, impact glasses, and melt rocks from the Lonar crater, India: Highly siderophile element systematics and Sr-Nd-Os isotopic signatures. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12665]
Published by arrangement with John Wiley & Sons

¹Paquette, J. A. et al. (>10)*
¹Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
*Find the extensive, full author and affiliation list on the publishers website

The calcium-aluminum-rich inclusions (CAIs) found in chondritic meteorites are probably the oldest solar system solids, dating back to 4567.30 ± 0.16 million years ago. They are thought to have formed in the protosolar nebula within a few astronomical units of the Sun, and at a temperature of around 1300 K. The Stardust mission found evidence of CAI-like material in samples recovered from comet Wild 2. The appearance of CAIs in comets, which are thought to be formed at lower temperatures and larger distances from the Sun, is only explicable if some mechanism allows the efficient transfer of such objects from the inner solar nebula to the outer solar nebula. Such mechanisms have been proposed such as an X-wind or turbulence. In this work, particles collected from within the coma of comet 67P/Churyumov–Gerasimenko are examined for compositional evidence of the presence of CAIs. COSIMA (the Cometary Secondary Ion Mass Analyzer) uses secondary ion mass spectrometry to analyze the composition of cometary dust captured on metal targets. While CAIs can have a radius of centimeters, they are more typically a few hundred microns in size, and can be smaller than 1 μm, so it is conceivable that particles visible on COSIMA targets (ranging in size from about 10 μm to hundreds of microns) could contain CAIs. Using a peak fitting technique, the composition of a set of 13 particles was studied, looking for material rich in both calcium and aluminum. One such particle was found.

Reference
Paquette JA et al. (2016) Searching for calcium-aluminum-rich inclusions in cometary particles with Rosetta/COSIMA. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12669]
Published by arrangement with John Wiley & Sons

^1,2Nicole G. Lunning, ¹Catherine M. corrigan, ²Harry Y. McSween, ^3,4Travis J. Tenner, ³Noriko T. Kita, ⁵Robert. J. Bodnar
¹Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996, USA
²Department of Mineral Sciences, Smithsonian Institution, National Museum of Natural History, Washington, DC 20560, USA
³Department of Geosciences, University of Wisconsin, Madison, WI 53706, USA
⁴Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA
⁵Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA

Volatile-rich and typically oxidized carbonaceous chondrites, such as CV and CM chondrites, potentially respond to impacts differently than do other chondritic materials. Understanding impact melting of carbonaceous chondrites has been hampered by the dearth of recognized impact melt samples. In this study we identify five carbonaceous chondrite impact melt clasts in three host meteorites: a CV3red chondrite, a CV3oxA chondrite, and a regolithic howardite. The impact melt clasts in these meteorites respectively formed from CV3red chondrite, CV3oxA chondrite, and CM chondrite protoliths. We identified these impact melt clasts and interpreted their precursors based on their texture, mineral chemistry, silicate bulk elemental composition, and in the case of the CM chondrite impact melt clast, in situ measurement of oxygen three-isotope signatures in olivine. These impact melts typically contain euhedral-subhedral olivine microphenocrysts, sometimes with relict cores, in glassy groundmasses. Based on petrography and Raman spectroscopy, four of the impact melt clasts exhibit evidence for volatile loss: these melt clasts either contain vesicles or are depleted in H2O relative to their precursors. Volatile loss (i.e., H2O) may have reduced the redox state of the CM chondrite impact melt clast. The clasts that formed from the more oxidized precursors (CV3oxA and CM chondrites) exhibit phase and bulk silicate elemental compositions consistent with higher intrinsic oxygen fugacities relative to the clast that formed from a more reduced precursor (CV3red chondrite). The mineral chemistries and assemblages of the CV and CM chondrite impact melt clasts identified here provide a template for recognizing carbonaceous chondrite impact melts on the surfaces of asteroids.

Reference
Lunning NG, Corrigan CM, McSween HY, Tenner TJ,Kita NT, Bodnar RJ (2016) CV and CM Chondrite Impact Melts. Geochmica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.05.038]
Copyright Elsevier

The most popular papers on Cosmochemistry Papers in May were:

1-Comelli D et al. (2016) The meteoritic origin of Tutankhamun’s iron dagger blade. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12664]

2-Cotto-Figueroa D, Asphaug E, Garvie LAJ, Rai A, Johnston J, Borkowski L, Datta S, Chattopadhyay A, Morris MA (2016) Scale-Dependent Measurements of Meteorite Strength: Implications for Asteroid Fragmentation. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.003]

3-Needham AW, Messenger S, Han J, Keller LP (2016) Corundum-hibonite inclusions and the environments of high temperature processing in the early solar system. Geochmica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.022]

4-Simon JI, Matzel JEP, Simon SB, Ross DK, Weber PK, Grossman L (2016) Oxygen isotopic variations in the outer margins and Wark-Lovering rims of refractory inclusions. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.025]

5-Robinson KL, Barnes JJ, Nagashima K, Thomen A, Franchi IA, Huss GR, Anand M, Taylor GJ (2016) Water in evolved lunar rocks: Evidence for multiple reservoirs. Geochimica et Cosmochmica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.05.030]

¹D. Ray, ¹S. Ghosh, ²T.K. Goswami, ³M.J. Jobin
¹PLANEX, Physical Research Laboratory, Ahmedabad 380 009, India
²Department of Applied Geology, Dibrugarh University, Assam, India
³Department of Applied Geology, Pondicherry University, India

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Ray D, Ghosh S, Goswami TK, Jobin MJ (2016) Insights into chondrule formation process and shock-thermal history of the Dergaon chondrite (H4-5). Geoscience Frontiers (in Press)
Link to Article [doi:10.1016/j.gsf.2016.02.005]

¹Arvidson RE et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website
¹Department of Earth and Planetary Sciences, Washington University in Saint Louis, St. Louis, Missouri 63130, U.S.A.

Mars Reconnaissance Orbiter HiRISE images and Opportunity rover observations of the ~22 km wide Noachian age Endeavour Crater on Mars show that the rim and surrounding terrains were densely fractured during the impact crater-forming event. Fractures have also propagated upward into the overlying Burns formation sandstones. Opportunity’s observations show that the western crater rim segment, called Murray Ridge, is composed of impact breccias with basaltic compositions, as well as occasional fracture-filling calcium sulfate veins. Cook Haven, a gentle depression on Murray Ridge, and the site where Opportunity spent its sixth winter, exposes highly fractured, recessive outcrops that have relatively high concentrations of S and Cl, consistent with modest aqueous alteration. Opportunity’s rover wheels serendipitously excavated and overturned several small rocks from a Cook Haven fracture zone. Extensive measurement campaigns were conducted on two of them: Pinnacle Island and Stuart Island. These rocks have the highest concentrations of Mn and S measured to date by Opportunity and occur as a relatively bright sulfate-rich coating on basaltic rock, capped by a thin deposit of one or more dark Mn oxide phases intermixed with sulfate minerals. We infer from these unique Pinnacle Island and Stuart Island rock measurements that subsurface precipitation of sulfate-dominated coatings was followed by an interval of partial dissolution and reaction with one or more strong oxidants (e.g., O2) to produce the Mn oxide mineral(s) intermixed with sulfate-rich salt coatings. In contrast to arid regions on Earth, where Mn oxides are widely incorporated into coatings on surface rocks, our results demonstrate that on Mars the most likely place to deposit and preserve Mn oxides was in fracture zones where migrating fluids intersected surface oxidants, forming precipitates shielded from subsequent physical erosion.

Reference
Arvidson RE et al. (2016) High concentrations of manganese and sulfur in deposits on Murray Ridge, Endeavour Crater, Mars. American Mineralogist 101, 1389-1405
Link to Article [http://dx.doi.org/10.2138/am-2016-5599]
Copyright: The Mineralogical Society of America

¹E. Bisceglia, ^1,2G. Micca Longo, ^1,2,3S. Longo
¹Dipartimento di Chimica, Università degli Studi di Bari, via Orabona 4, I-70126 Bari, Italy
²CNR-NANOTEC, Bari section, via Amendola 122/D, I-70126 Bari, Italy
³INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy e-mail:

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Bisceglia E, Longo GM, Longo S (2016) Thermal decomposition rate of MgCO3 as an inorganic astrobiological matrix in meteorites. International Journal of Astrobiology (in Press)
Link to Article [http://dx.doi.org/10.1017/S1473550416000070]

¹G.M. Marion, ²D.C. Catling, ³J.S. Kargel, ⁴J.K. Crowley
¹Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA.
²Department of Earth & Space Sciences, University of Washington, Seattle, WA 98195, USA.
³Department of Hydrology & Water Resources, University of Arizona, Tucson, AZ 85721, USA.
⁴P.O. Box 344, Lovettsville, VA 20180, USA.

On Mars, evidence indicates widespread calcium sulfate minerals. Gypsum (CaSO4•2H2O) seems to be the dominant calcium sulfate mineral in the north polar region of Mars. On the other hand, anhydrite (CaSO4) and bassanite (CaSO4•0.5H2O) appear to be more common in large sedimentary deposits in the lower latitudes. The tropics are generally warmer and drier, and at least locally show evidence of acidic environments in the past. FREZCHEM is a thermodynamic modeling tool used for assessment of equilibrium involving high salinity solutions and salts, designed especially for low temperatures below 298 K (with one version adapted for temperatures up to 373 K), and we have used it to investigate many Earth, Mars, and other planetary science problems. Gypsum and anhydrite were included in earlier versions of FREZCHEM and our model Mars applications, but bassanite (the CaSO4 hemihydrate) has not previously been included. The objectives of this work are to (1) add bassanite to the FREZCHEM model, (2) examine the environments in which thermodynamic equilibrium precipitation of calcium sulfate minerals would be favored on Mars, and (3) use FREZCHEM to model situations where metastable equilibrium might be favored and promote the formation or persistence of one of these phases over the others in violation of an idealized equilibrium state.

We added a bassanite equation based on high temperatures (343 to 373 K). A Mars simulation was based on a previously published Na-Ca-Mg-Cl-SO4 system over the temperature range of 273 to 373 K. With declining temperatures, the first solid phase under equilibrium precipitation is anhydrite at 373 K, then gypsum forms at 319 K (46 °C), and epsomite (MgSO4•7H2O) at 277 K. This sequence could reflect, for example, the precipitation sequence in a saturated solution that is slowly cooled in a deep, warm aquifer.

Because FREZCHEM is based on thermodynamic equilibrium, a crude approach to problems involving metastable equilibria is available by removing phases that may have kinetically inhibited formation. Removing anhydrite allows bassanite to precipitate at 373 K, followed by gypsum at 351 K (78 °C), and epsomite at 277 K. Removing anhydrite and gypsum allows bassanite to form from 373 to 273 K. But bassanite formation from warm to cold temperatures does not seem appropriate for Mars and Earth.

An explanation for spatial patterns of gypsum, anhydrite, and bassanite on Mars and Earth could be past environmental differences. Anhydrite and bassanite are favored near Mars’ equator with higher temperatures, along with drier, more saline, and more acidic environments. Gypsum would be favored at the lower temperatures in the Mars polar region with wetter, lower salinity, and less acidic environments. On Earth, Ca-sulfate would likely over time largely finish re-precipitating as the more insoluble gypsum. But Mars was not in long-term moderate climates compared to Earth that strongly influenced the dominance of gypsum on Earth. So while temperature and water/acid environments for CaSO4 minerals on Mars may have been a major factor for these precipitations, the short-term moderate climates on Mars may also have influenced the prevalence of higher soluble CaSO4 species in the lower Mars latitudes.

Reference
Marion GM, Catling DC, Kargel JS, Crowley JK (2016) Modeling Calcium Sulfate Chemistries with Applications to Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.016]
Copyright Elsevier